You are trying to change the leader of a group or network/ministry, but when you go to the the drop down menu, you are not finding the name of the person you want!! So what now??
Usually, this happens because you have not change the role of this person. If the person you want is listed as member, then it will not show on the drop down menu.
For groups: it will only show the role leader and above. Go the person's profile page, click on edit and change the role to leader or above.
For Networks/Ministry: It will only show the role discipler and above. Go the person's profile page, click on edit and change the role to discipler or above.
Go back now and it show on the drop down menu.